Medical devices include devices designed to be implanted into a patient. Some examples of these implantable medical devices (IMDs) include cardiac function management (CFM) devices such as implantable pacemakers, implantable cardioverter defibrillators (ICDs), cardiac resynchronization therapy devices (CRTs), and devices that include a combination of such capabilities. The devices can be used to treat patients or subjects using electrical or other therapy or to aid a physician or caregiver in patient diagnosis through internal monitoring of a patient's condition. The devices may include one or more electrodes in communication with one or more sense amplifiers to monitor electrical heart activity within a patient, and often include one or more sensors to monitor one or more other internal patient parameters. Other examples of IMDs include implantable diagnostic devices, implantable drug delivery systems, or implantable devices with neural stimulation capability.
Medical devices also include ambulatory or wearable medical devices (WMDs) such as wearable cardioverter defibrillators (WCDs). WCDs are monitors that include surface electrodes. The surface electrodes are arranged to provide one or both of monitoring surface electrocardiograms (ECGs) and delivering cardioverter and defibrillator shock therapy. Some medical devices include one or more sensors to monitor different physiologic aspects of the patient. For example, the devices may derive measurements associated with a cardiac depolarization of the patient. Such measurements can provide useful information concerning the cardiac health of the patient.
By monitoring cardiac signals indicative of expansions or contractions, IMDs can detect abnormally slow heart rate, or bradycardia. In response to an abnormally slow heart rate some CFM devices deliver electrical pacing stimulation energy to induce cardiac depolarization and contraction. The pacing stimulation energy is delivered to provide a depolarization rate that improves hemodynamic function of the patient. Delivery of pacing therapy should be optimized to ensure therapy delivery and yet avoid unnecessary stress on the heart and unnecessary reduction of battery life. Optimal selection of the site for delivery of the pacing therapy can be part of pacing therapy optimization. Optimal site selection can lead to optimized use of pacing energy and to improved hemodynamic function of the patient or subject.
Monitoring cardiac signals may also detect abnormalities in the synchronization of contractions between the left and right sides of the heart. These abnormalities are sometimes treated with an IMD that delivers cardiac resynchronization therapy (CRT).